Process for upgrading malathion



United States Patent 3,440,305 PROCESS FOR UPGRADING MALATHION Ralph Dettmer Divine, Rahway, N.J., assignor to American Cyanamid Company, Stamford, Conn., a corporation of Maine No Drawing. Filed Sept. 30, 1965, Ser. No. 491,807 Int. Cl. C07f 9/16 US. Cl. 260-990 9 Claims ABSTRACT OF THE DISCLOSURE Upgraded technical malathion containing not more than 0.5% diethyl fumarate, prepared by washing technical malathion with an aqueous water-soluble sulfur compound, such as sodium sulfide or potassium sulfite, is provided.

The present invention relates to an improved technical malathion and to a process for preparing the same. More particularly, it relates to an up-graded technical malathion containing from about 0.001% to not more than 0.5% diethyl fumarate and has for its principal object the provision for preparing the same utilizing a novel aqueous wash procedure.

Malathion or the 0,0-dimethyl phosphorodithioate of diethyl mercaptosuccinate is a well-known pesticide which can be prepared by reacting 0,0-dimethyl phosphorodithioic acid with diethyl maleate as described with greater particularity in US. Letters Patent No. 2,578,658. When so prepared, the pesticide is better known as technical malathion and contains a maximum of about impurities which result from the reaction. One such impurity is 0,0-dimethyl phosphorodithioic acid and another impurity is the isomer of diethyl maleate, namely, diethyl fumarate. Usually, diethyl fumarite is present as an impurity to the extent of from about 2% to about 4% of the over-all technical malathion content.

Attempts have been made in the past to upgrade technical or commercially prepared malathion. Illustrative procedures are described, for instance, in US. Letters Patent Nos. 2,879,284 (which relates to a peroxide or hydroperoxide treatment of malathion) and 2,980,723 (which is directed to an ozone treatment of malathion). Such procedures, while markedly improving the typical mercaptan-like odor of technical malathion, unfortunately, do not improve the diethyl fumarate content to a level of 0.5%, or less. The upgrading of ozonized technical malathion to the indicated level has become increasingly more significant due to the recent volume-wise handling of technical malathion by untrained personnel such as, for instance, pilots adept in the large acreage application of low-volume technical malathion. When such persons are exposed to continuous and prolonged periods of use, a skin sensitization or irritation may develop apparently attributable to the diethyl fumarate impurity in amounts ranging from 2% to 4% normally present in technical malathion. However, even at levels as low as 0.75% of diethyl fumarate, significant numbers of persons are topically affected adversely. Accordingly, if an upgraded technical malathion which is non-dermatitic and nonsensitizing could be provided by a simple, straightforward and economical process, such a product would amount to a substantial advance in the pesticidal art.

In accordance with the present invention, it has been found that the diethyl fumarate content in technical malathion which has been prepared by the hereinabove-referred to prior art procedures can be reduced to a level which would render malathion, as commercially prepared, non-dermatitic and non-sensitizing to those who may handle this pesticide. The marked percentage-wise reduction of diethyl fumarate is accomplished in a straightfor- 3,440,305 Patented Apr. 22, 1969 ward and economical manner by subjecting technical malathion to an aqueous wash containing relatively small amounts of an inorganic water-soluble sulfur compound and, thereafter, recovering the water-insoluble up-graded technical malathion which is found to contain from about 0.001% to not more than 0.5 of diethyl fumarate.

In a preferred embodiment a water-insoluble technical malathion is washed with an aqueous solution containing a sufiicient amount of a water-soluble ammonium or alkali metal sulfide or sulfite to obtain an over-all pH level between not less than 7 and 12, or higher. In washing the malathion to be treated, the mixture is vigorously stirred for a period of from about 15 minutes to about two hours. Thereafter, there is effected a separation of the organic phase containing malathion from the inorganic phase containing a major amount of impurities. Upon polarographic analysis, the diethyl fumarate content remaining in the so-treated malathion is not more than about 0.5%, at which level a non-dermatitic, non-sensitizing technical malathion of improved color and odor is obtained.

Technical malathion subjected to the process of the invention can be employed either as untreated malathion which emanates directly from the reaction vessel or is one pretreated in accordance with any of the prior art practices as, for instance, by ozonization. In either case, technical malathion contains a level of diethyl fumarate which to some individuals can be considered to be substantially dermatitic and sensitizing, since the desired level is higher than 0.5 of the diethyl fumarate.

In general, there is employed equal weights of (a) technical malathion (which is in the form of an oily liquid) and (b) an aqueous solution containing the inorganicsulfide or sulfite referred to above by providing between about 1% and about 10% of said sulfide or sulfite in the aqueous salt solution. There is then obtained an over-all pH between about 7 and about 12 and is adjusted preferably between 8.5 and 10 by introducing varying amounts of the inorganic salt dependent upon the quantity of acids present in the oil. Not only is the diethyl fumarate content substantially reduced, but impurities, such as the 0,0-dimethyl phosphorodithioic acid, are removed in the aqueous phase. The water-soluble salt of any resultant phosphorodithioic acid derivative is formed upon neutralization. If desired, the washing treatment may be repeated for a plurality of operations so as to further remove diethyl fumarate and water-soluble impurities.

The technical malathion to be treated and the inorgarlic salt solution are vigorously agitated to insure that the impurities present in the mixture separate from the organic phase enter the aqueous phase when permitting the mixture to come to rest. The organic phase is separated from the aqueous phase by any well-known means utilizing, for instance, a separatory funnel.

In general, the temperature involved in the washing step described above may widely vary from about room temperature to about C. It is preferred, however, to operate for optimum results at a temperature between about 50 C. and 60 C., since at the higher temperatures a relatively short interval, usually between 20 minutes and 30 minutes, can be employed for effecting maximization of the desired reduction of diethyl fumarate content.

The following examples will illustrate the invention. These are not to be taken as limitative. Unless otherwise specified, the parts are by weight.

Example 1 To a suitable separatory funnel are added equal weights of (a) malathion having a cherry-red coloration and containing 1.14% diethyl fumarate and (b) an aqueous solution containing 3% sodium sulfide. The mixture is agitated vigorously at 50 C.-60 C. for twenty-five minutes. The crude malathion is thereafter separated from the aqueous layer which is discarded. To the separated organic portion is next added an equal volume of water. That mixture is then agitated for several minutes. Thereafter, the latter is permitted to settle and the aqueous phase separated from the organic phase. Resultant crude organic layer is then dried by stripping the same at a reduced pressure of mm. Hg. and at a temperature of 88 C.

The product recovered, upgraded technical malathion of 98% yield, possesses a straw coloration assaying at 99.0% and analyzes as containing a diethyl fumarate content of 0.05%.

Repeating the above procedure in every respect except that the so-prepared technical malathion is employed, a product analyzing as 0.001% diethyl fumarate is obtaine in good yield.

Examples 2-6 Technical malathion assaying as 95.5% and containing a diethyl fumarate content of 2.5% is washed in a suitable vessel with an equal weight of an aqueous solution of each of several selective reagents listed in Table I below at between 50 C. and 60 C. for thirty minutes at a pH beween about 8.7 and 10.3, allowing the mixture to settle so as to effect the separation of the two resulting phasesflhe inorganic phase is then separated and further washed with an equal weight of water, allowing the mixture to settle and effecting a further separation of the resulting phases. Finally, the organic layer is next stripped under vacuum of mm. Hg at 80 C.

Resultant product is analyzed polarographically for diethyl fumarate. The data are set forth in the table below.

necessary to irritate the skin prior to the application of each inductive path. This was done by holding a 5% aqueous solution of sodium lauryl sulfate in contact with the test site for 24 hours, after which the inductive patch with malathion in petrolatum was applied for 48 hours. This 72-hour cycle was repeated for a total of five times. In all other respects, the test technique was identical with that described above for diethyl fumarate.

The results of these tests appear in Table II below.

TABLE II It will be noted that there is a striking correlation between concentration of diethyl fumarate and sensitization ratio. The table also indicates that very low concentrations of diethyl fumarate induce skin sensitization in a significantly large number of subjects. Thus, diethyl fumarate is an unusually potent skin sensitizer. This table further indicates that when the diethyl fumarate content is reduced below 0.5% there is provided a product which, for practical purposes, is non-sensitizing and non-dermatitic to a substantial number of individuals. Similarly, the treated technical malathion of the present invention can be advantageously utilized in formulations usually as dust TABLE 1 Example No.

Technical malathion tested wlth Sodium Sodium Potassium Potassium Ammonium sulfide sulfite sulfide sulfite sulfide Amount used, g. 10 10 10 10 Water used, g 190 190 190 190 Percent reagent 3 5 5 5 5 Malathion washed, grams 200 200 200 200 200 Temperature wash, C- -60 50-60 50-60 50-60 50-00 Organic separated, g. 198 197 I 200 203 193 Stripped organic, g 191 192 194 192 191 Assay, percent 98. 5 97.2 99. 9 97. 0 96. 7 DEF, percent 0. 16 0. 22 0. 5 0. 12 0. 10

Example 7 With respect to sensitization tests utilizing diethyl fumarate it was determined that diethyl fumarate is a primary irritant to intact skin. Therefore, pretreatment of the test sites was not necessary.

Diethyl fumarate was mixed with petrolatum in the various concentrations at which it was desired to perform the tests. Approximately one gram of petrolatum containing the desired concentration of diethyl fumarate was placed on a patch of fabric and this was applied to the skin of each of twenty-five test subjects per test. The patches were held snugly in place by a plastic tape of impervious material. After 48 hours of contact, the patches were removed and new identical patches were applied to the same skin site for another 48 hours. This cycle was repeated for a total of five applications (known as induction phase). After the fifth patch was removed, the subject was given a rest period of two weeks.

At the end of that time a challenge patch was applied to a site distant from that used for the induction series. For this patch, a concentration of diethyl fumarate in petrolatum was chosen that was known to be not primarily irritant. After 48 hours, the test site was examined and the severity of the reaction was graded. Test establishes that substantial numbers of subjects are sensitized by diethyl fumarate.

With respect to the sensitization tests with the various samples of malathion, very high purity malathion had been found not to be a primary irritant. Therefore, it was concentrates, dilute dusts, liquid concentrates and as wettable powders, whereby such formulations are found to be non-sensitizing and non-dermatitic.

I claim:

1. A process for preparing technical malathion containing from 0.001% to not more than 0.5 diethyl fumarate which comprises the steps of: admixing technical malathion with an aqueous solution of a reagent selected from the group consisting of sodium sulfide, sodium sulfite, potassium sulfide, potassium sulfite, ammonium sulfide and ammonium sulfite to establish a pH of at least 7 in said mixture; effecting the separation of the two resulting phases; and recovering an organic phase which contains washed technical malathion of markedly reduced diethyl fumarate content.

2. A process according to claim 1 wherein the temperature for effecting the washing operation is maintained at between about room temperature and about 75 C.

3. A process according to claim 1 wherein the washing step is carried out at a temperature between about 50 C. and 60 C.

4. A process according to claim 1 wherein the technical malathion being treated and the aqueous solution containing reagent are present in an equal weight relationship.

5. A process according to claim 1 wherein the aqueous."

wash solution contains about 1% to about 10% by weight of sodium sulfide. 6. A process according to claim 1 wherein the aqueous 5 wash solution contains about 1% to about 10% by weight of sodium sulfide.

7. A process according to claim 1 wherein the aqueous wash solution contains about 1% to about 10% by weight of potassium sulfide.

8. A process according to claim 1 wherein the aqueous wash solution contains about 1 %to about 10% by weight of potassium sulfite.

9. A process according to claim 1 wherein the aqueous wash solution contains about 1% to about 10% by weight 10 of ammonium sulfide.

References Cited UNITED STATES PATENTS 2,578,652 12/1951 Cassaday 260'942 3,098,866 7/1963 Divine 260-990 XR CHARLES B. PARKER, Primary Examiner.

ANTON H. SUTTO, Assistant Examiner.

US. Cl. X.R. 260-942; 424-213 U.S. DEPARTMENT OF COMMERCE PATENT OFFICE Washington, D.C. 20231 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,440, 305 April 22 196 Ralph Dettmer Divine It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

"2,578,658" should read 2 ,578,652 line 36,

Colunm 1, line 29,

Column 4 line 2, "path" should fumarite" should read fumarate read patch (SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents 

